Illuminated pushbutton switches and indicators utilized in modern avionics systems must operate over a wide range of ambient lighting environments, such as daylight, nighttime and even night vision goggle (NVG) conditions. Traditionally such illuminated switches and indicators used simple voltage control to vary the illumination intensity (or brightness) of the displays, with a different voltage being supplied to the display based upon the desired illumination level for the respective ambient lighting environment.
Unfortunately, many digital avionics systems do not have the capability to supply a varying (analog) voltage to alter the illumination of switches and indicators. Some digital avionics systems do incorporate pulse width modulation (PWM) capabilities, but the rapid and often narrow digital pulses used with this technique have been found to generate unacceptable levels of Electromagnetic Interference (EMI) or Radio Frequency Interference (RFI).
There is, therefore, a need in the art for improved voltage controlled dimming.